Directions

Adjust oven rack to middle position and heat oven to 350 degrees. Fold two 12-inch pieces foil lengthwise so each measures 7 inches wide. Fit 1 sheet into 8-inch-square baking dish, pushing foil into corners and up sides of pan (overhang will help in removal of brownies). Repeat with second sheet, placing in pan perpendicular to first sheet. Spray foil with cooking spray. Whisk flour, cocoa, baking powder, and salt together in medium bowl. Melt bittersweet chocolate and butter in large bowl until smooth . Cool 2 to 3 minutes, then whisk in sour cream, chocolate syrup, vanilla, egg, egg white, and sugar. Using rubber spatula, fold dry ingredients into chocolate mixture until combined. Batter will be very thick. Pour batter into pan, spread into corners, and level surface with spatula. Bake until slightly puffed and toothpick inserted in center comes out with a few sticky crumbs attached, 20 to 25 minutes. Cool brownies completely in pan on wire rack, at least 1 hour. Remove brownies from pan using foil handles. Cut into 2-inch squares and serve.